Firewall helps to keep attackers or external threats from getting access to your system in the first place. Most people are aware that worms often travel through email. They generally arrive as an attachment to an email that the user is enticed to click on by the text of the email itself. We call these threats “mass-mailing worms.” The best thing to do with these threats is simply to delete the email and not click on the attachment. This is exactly where a firewall can help protect you. The firewall monitors all network traffic and has the ability to identify and block unwanted traffic. Since most computers these days are connected to the Internet, attackers have many opportunities to find victim computers. These attackers probe other computers on the Internet to determine if they are vulnerable to various types of attacks. When they find a suitable computer, they can compromise it and insert themselves onto that computer. At that point the attacker can make the victim computer perform almost any task he desires. Attackers will often try to steal personal information for the purposes of financial fraud. All of this activity takes place in the background without the user knowing what is happening.
